1. Field of the Invention
The present invention relates to an electrochemical capacitor.
2. Description of the Related Art
There has heretofore been known an electric double-layer capacitor having positive and negative electrode elements disposed in confronting relation to each other with a separator interposed therebetween. Each of the positive and negative electrode elements having a solid electrode made of activated carbon on the surface of a current collector such as of metal foil or the like. The positive and negative electrode elements are sealed together with an electrolytic solution in a casing which has terminals connected to the respective current collectors.
In the above conventional electric double-layer capacitor, the solid electrode is made of activated carbon as a substance having a large specific surface area. However, the electric double-layer capacitor having solid electrodes of activated carbon has an energy density lower than secondary cells that operate based on a chemical reaction. In view of such a drawback, there has been proposed an electrochemical capacitor having solid electrodes made of a material which is capable of producing pseudocapacitance owing to an electrochemical reaction. Various materials including ruthenium oxide capable of producing pseudocapacitance have been reviewed for use as solid electrode materials. However, these materials are disadvantageous in that they are expensive.